Integrated balun and transformer structures

ABSTRACT

A method for producing an on-chip signal transforming device. The method includes providing a substrate, and laying a first conductive layer above the substrate, wherein the first conductive layer has a plurality of interleaved inductors. The method then includes laying a second conductive layer above the substrate, wherein the second conductive layer has at least one inductor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to integrated circuitdevices, and, more particularly, to baluns and transformers manufacturedon integrated circuit chips.

[0003] 2. Description of Related Art

[0004] Increasingly, due to reliability, performance and costconsiderations, devices that previously resided on a printed circuitboard (PCB) are being integrated into an integrated circuit (IC) chip.Transformers, inductors, and baluns are examples of devices that havemigrated to the IC chip.

[0005] Due to the relatively noisy environment on an IC chip, manysignals on a chip are typically differential or double-ended signals.Differential signals offer good common-mode rejection of noise; noisetypically affects both halves of the differential signal in the samemanner, and since information is contained in the difference of bothsignal halves, the difference does not change appreciably despite thenoise that has been added to both halves.

[0006] A balun is an example of a device that accepts a single-endedsignal and transforms it into a differential signal and vice versa. Theterm balun suggests its function: conversion of balanced (differential)signals to unbalanced (single-ended) signals. Signals on PCBs aretypically single-ended signals. Since IC chips use differential signals,baluns have been placed on PCBs to transform a single-ended signal intoa differential signal. Baluns have also been placed on IC chips.However, present designs suffer from asymmetrical parasiticcharacteristics (e.g., asymmetric parasitic capacitances andresistances) and poor magnetic coupling. The asymmetrical parasiticcharacteristics cause a differential signal to be asymmetrical. Symmetryin a differential signal is very important to the proper functioning ofmany differential circuits. Furthermore, poor magnetic coupling resultsin inefficient energy transfer.

[0007] A transformer is another example of a device that has on-chipuses. For example, a transformer can be used to match impedances betweenamplifier stages while providing DC isolation between the stages. Atransformer for differential signals also needs to offer good magneticcoupling as well as symmetrical parasitic characteristics. Presentdesigns do not offer relatively good parasitic characteristics and goodmagnetic coupling.

[0008] Thus, there is a need for baluns and transformers that provideimproved symmetry and magnetic coupling.

SUMMARY OF THE INVENTION

[0009] A method for producing an on-chip signal transforming device isdescribed. The method includes providing a substrate and laying a firstconductive layer above the substrate, wherein the first conductive layerhas a plurality of interleaved inductors. The method then includeslaying a second conductive layer above the substrate, wherein the secondconductive layer has at least one inductor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings in which likereferences denote similar elements, and in which:

[0011]FIG. 1a illustrates an electrical circuit representation of abalun;

[0012]FIG. 1b illustrates a balun according to one embodiment of thepresent invention;

[0013]FIG. 2 illustrates a balun according to yet another embodiment ofthe present invention;

[0014]FIG. 3a illustrates a balanced transformer according to oneembodiment of the present invention;

[0015]FIG. 3b illustrates an electrical circuit representation oftransformer 300;

[0016]FIG. 3c illustrates two amplifiers coupled by a balanced linetransformer;

[0017]FIG. 4a illustrates another balun according to one embodiment ofthe present invention, which has the capability to transform adifferential signal to a single ended signal and vice-versa; and

[0018]FIGS. 4b(1-3), and 4 c illustrate three layers used to make theinductors of the balun illustrated in FIG. 4a.

DETAILED DESCRIPTION

[0019] Methods and apparatus for integrated transformers and baluns aredescribed. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the present invention. However, one skilled in the artwill appreciate that the present invention may be practiced in a varietyof circuits, especially radio frequency circuits, without these specificdetails. In other instances, well-known operations, steps, functions anddevices are not shown in order to avoid obscuring the invention.Repeated usage of the phrases “in one embodiment,” “an alternativeembodiment,” or an “alternate embodiment” does not necessarily refer tothe same embodiment, although it may.

[0020]FIG. 1a illustrates an electrical circuit representation of abalun. Balun 100 includes inductors 114 and inductors 108 and 110.Inductors 108 and 110 are dc (direct current) decoupled from andmagnetically coupled with inductor 114 permitting the transfer ofenergy. Balun 100 can convert the signal of unbalanced transmission line102 into to a signal of balanced transmission lines 104 and 106. Balun100 can also convert a signal of balanced transmission lines 104 and 106to a signal of unbalanced transmission line 102. One advantage of thebalanced portion is that external noise affects the lines of thebalanced transmission equally without appreciably affecting thepotential difference in lines 104 and 106. While the electric circuitrepresentation for a balun has been known for a long time, the designsfor integrated baluns and transformers of the present invention haveheretofore been unkown.

[0021]FIG. 1b illustrates a balun according to one embodiment of thepresent invention. Balun 100 includes two interleaved inductors 108 and110 in metal layer 108′ and vertically displaced spiral inductor 114 inmetal layer 114′, all of them above substrate 116. Making inductors 108and 110 interleaved causes each of the inductors to have substantiallyequivalent parasitic characteristics; in other words they aresymmetrical. Furthermore, having the interleaved inductors stacked aboveinductor 114 provides for relatively better magnetic coupling incomparison to a lateral coupling arrangement in which interleavedinductors of a primary winding are placed adjacent to and in the samelayer as the inductor of a secondary winding.

[0022] While in the above description, balun 100 has interleavedinductors 108 and 110 above spiral inductor 114, in an alternativeembodiment spiral inductor 114 is above interleaved inductors 108 and110.

[0023]FIG. 2 illustrates a balun according to yet another embodiment ofthe present invention. Balun 200 includes two interleaved inductors 208and 210 in metal layer 208′ and vertically displaced spiral inductor 214in metal layers 214′ and 214″, all of them above substrate 216. A firstportion of inductor 214 is in layer 214′ and a second portion ofinductor 214 is in layer 214″. Having an inductor which has twice thenumber of windings of inductor 114 split among two layers results in aninductor with a larger inductance, which can be desirable in someinstances because it results in larger magnetic coupling.

[0024]FIG. 3a illustrates a transformer according to one embodiment ofthe present invention. Transformer 300 includes stacked interleavedinductors 308 and 314 in metal layers 308′ and 314′ respectively.Interleaved inductor 308 includes spiral inductors 308 a and 308 b.Interleaved inductor 314 includes spiral inductors 314 a and 314 b. Thestacked interleaved structure provides good magnetic coupling betweeninductors 308 and 314 and symmetric parasitic characteristics between308 a and 308 b, as well as between 314 a and 314 b. FIG. 3b illustratesan electrical circuit representation of transformer 300. A transformersuch as transformer 300 is desirable because it can be used, forexample, to match impedances between amplifier stages while providing DC(direct current) isolation between the stages. FIG. 3c illustrates twoamplifiers coupled by a balanced line transformer. Because of the DCisolation between amplifier 320 and amplifier 324, amplifer 320's outputcan be set to a bias voltage V_(A) and amplifier 324's input can be setto a different bias voltage V_(B).

[0025]FIG. 4a illustrates another balun according to one embodiment ofthe present invention, which has the capability to transform adifferential signal to a single ended signal and vice-versa. Transformer400 includes inductors 408, 410 and 414. As shown in FIG. 4b 1, theinductors 408 and 410 are interleaved to provide good magnetic couplingbetween them. According to one embodiment, they are disposed in the samelayer except at areas 420 a-1, and 420 a-2 were one inductor crossesover the other. In one embodiment illustrated in FIG. 4b 2, inductor 408is entirely disposed on metal layer 408′, with inductor 410 crossinginductor 408 using vias 422 that electrically connect to another metallayer 410′ above or below the metal layer 408.′ In the embodiment shownin FIG. 4b 2, inductor 408 makes two right angle turns at the cross overarea 420 a-1, and although not shown in FIG. 4b 2, inductor 410 alsomakes two right angle turns at the cross over area 420 a-2. In theembodiment shown in FIG. 4b 3, inductor 410 crosses over inductor 408 atan angle, such as, for example, 45 degrees or some other angle. Further,as shown in FIG. 4c inductor 414 is stacked on a different metal layer414′, disposed adjacent to one of layers 408′ and 410′, and allowsinductor 414 to couple to each of inductors 408 and 410.

[0026] In a modified embodiment, inductors 408 and 410 can be disposedin separate metal layers 408′ and 410′, respectively. In the embodiment,since the inductors are on separate layers, a cross over is notrequired, although turns within a layer can be made within a layer toequalize coupling between inductors 408 and 410.

[0027] Thus, methods and apparatus for integrated baluns andtransformers have been described. Although the present invention hasbeen described with reference to specific exemplary embodiments, it willbe evident to one of ordinary skill in the art that variousmodifications and changes may be made to these embodiments withoutdeparting from the broader spirit and scope of the invention as setforth in the claims. Accordingly, the specification and drawings are tobe regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A method for producing an on-chip signaltransforming device, the method comprising: providing a substrate;laying a first conductive layer above the substrate, wherein the firstconductive layer has a plurality of interleaved inductors; and laying asecond conductive layer above the substrate and insulated from the firstconductive layer, wherein the second conductive layer has at least oneinductor.
 2. The method of claim 1, wherein the second conductive layeris below the first conductive layer.
 3. The method of claim 1, whereinthe at least one inductor is a plurality of interleaved inductors. 4.The method of claim 1, wherein the at least one inductor is a spiralinductor.
 5. The method of claim 1, further comprising laying a thirdconductive layer insulated from the first and second conductive layersand wherein the at least one inductor is partly in the third conductivelayer and the first conductive layer is in between the second conductivelayer and the third conductive layer.
 6. A method for producing anon-chip signal transforming device, the method comprising: providing asubstrate; laying a first conductive layer above the substrate, whereinthe first conductive layer has a plurality of interleaved inductors; andlaying a second conductive layer above the substrate insulated from thefirst conductive layer, wherein the second conductive layer has aplurality of interleaved inductors.
 7. A method for producing an on-chipsignal transforming device, the method comprising: providing asubstrate; laying a first conductive layer above the substrate, whereinthe first conductive layer has a plurality of interleaved inductors; andlaying a second conductive layer above the substrate insulated from thefirst conductive layer, wherein the second conductive layer has a firstpart of an inductor; laying a third conductive layer insulated from thefirst and second conductive layers; and wherein the inductor has asecond part in the third conductive layer, the first part and the secondpart are connected by way of a via and the first conductive layer is inbetween the second conductive layer and the third conductive layer.
 8. Amethod for producing an on-chip signal transforming device, the methodcomprising: providing a substrate; laying a first conductive layer abovethe substrate, wherein the first conductive layer has a first spiralinductor; and laying a second conductive layer above the substrateinsulated from the first conductive layer, wherein the second conductivelayer has at least a second spiral inductor, such that the first andsecond spiral inductors are interleaved.
 9. The method according toclaim 8 further including the step of: laying a third spiral inductor ona third conductive layer above the substrate and insulated from thefirst and second conductive layers, wherein the third conductive layerhas at least a third spiral inductor that couples to the first spiralinductor and the second spiral inductor.
 10. A method for producing anon-chip signal transforming device, the method comprising: providing asubstrate; laying a first conductive layer above the substrate, whereinthe first conductive layer has a first spiral inductor and a secondspiral inductor that are interleaved; and laying a second conductivelayer above the substrate insulated from the first conductive layer;providing a conductive path from the first conductive layer to thesecond conductive layer and back to the first conductive layer to allowthe first spiral inductor to cross over the second spiral inductor. 11.The method according to claim 10 further including the step of: laying athird spiral inductor on a third conductive layer above the substrateand insulated from the first and second conductive layers, wherein thethird conductive layer has at least a third spiral inductor that couplesto the first spiral inductor and the second spiral inductor.